GEF valves are 3-way temperature control valves consisting of a powerful rotary valve and a modulating EL actuator. GPD is the designation for the same valve body with pneumatic actuator.
GPD valves are 3-way temperature control valves consisting of a powerful rotary valve and a quarter turn PNEUMATIC actuator. GEF is the designation for the same valve body with EL actuator. The GG model is a newer design, but the same dimensions and functionality.